JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

15 Dec 1997

Volume 107, Issue 23, pp. 9715-10353

Page 1 of 3 Pages Next Page | Jump to Page

Electronic spectroscopy and molecular structure of jet-cooled diphenylamine and diphenylamine derivatives

I. V. Tretiakov and J. R. Cable

J. Chem. Phys. 107, 9715 (1997); http://dx.doi.org/10.1063/1.475268 (11 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
Vibrationally resolved electronic spectra of diphenylamine, three deuterated isotopomers, and both para-methyl and para-fluoro substituted derivatives have been recorded in a supersonic jet expansion using resonantly enhanced two-photon ionization. Analysis of these spectra, supported by ab initio calculations, has been used to determine the gas phase structure of diphenylamine. In both the ground and first excited singlet states, an effective C2 symmetry structure is found in which the nitrogen atom is in a planar configuration and the phenyl rings adopt equal torsional angles. Calculations suggest that large-amplitude motion along the nitrogen inversion coordinate is possible in the ground electronic state. Isotopic substitutions have been used to assign the two low-frequency Franck–Condon active modes to different admixtures of symmetric phenyl torsion and bending about the central nitrogen. Electronic excitation to the S1 state results in a decrease in the phenyl torsional angles of 7.4° and an increase in the C–N–C bond angle of 4.0°. While spectra of both the para mono- and dimethyl derivatives as well as the para-diflouro derivative indicate that little change occurs in either the physical or electronic structure of the basic chromophore, the spectrum of the monosubstituted para-fluoro derivative is indicative of a substantial perturbation to both. © 1997 American Institute of Physics.
Show PACS
33.20.Lg Ultraviolet spectra
31.15.A- Ab initio calculations
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.30.Gs Hyperfine interactions and isotope effects
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.-b Photon interactions with molecules
31.50.Df Potential energy surfaces for excited electronic states

Polarization selectivity of nonresonant spectroscopies in isotropic media

Robert L. Murry and John T. Fourkas

J. Chem. Phys. 107, 9726 (1997); http://dx.doi.org/10.1063/1.475269 (15 pages) | Cited 47 times

Full Text: | Download PDF

Show Abstract
We present an analysis of the contributions of the first- and second-derivative tensors of the many-body polarizability to third- and fifth-order nonresonant spectroscopies in isotropic media. Collision-induced effects are shown to have a notable influence on the second-derivative polarizability tensor (Π(2)) for intermolecular modes. As a result, polarization selectivity in nonresonant intermolecular spectroscopies can be achieved in fifth-order spectroscopies. Additionally, terms in fifth-order spectroscopy that arise from three interactions through Π(2) may not be negligible in many liquids. Our analysis shows that there exists no straightforward relationship between the observables in third- and fifth-order intermolecular spectroscopies. The predictions of this analysis are tested against the available experimental data for CS2. © 1997 American Institute of Physics.
Show PACS
78.20.Bh Theory, models, and numerical simulation
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.20.Gj Intermolecular and atom-molecule potentials and forces

Temperature dependence of vibrational lifetimes at the critical density in supercritical mixtures

D. J. Myers, R. S. Urdahl, Binny J. Cherayil, and M. D. Fayer

J. Chem. Phys. 107, 9741 (1997); http://dx.doi.org/10.1063/1.475270 (8 pages) | Cited 22 times

Full Text: | Download PDF

Show Abstract
Experimental measurements are reported for the temperature dependence of the vibrational lifetime, T1, of the asymmetric CO stretching mode of tungsten hexacarbonyl in supercritical ethane at constant density from just above the critical temperature to substantially higher temperatures. T1 is found initially to increase with temperature along an isochore (reaching a maximum at about 70° above the critical point of ethane), and then subsequently to decrease. Using a recent classical theory of vibrational relaxation, we attempt to rationalize the T1 data. This behavior can be semiquantitatively reproduced by the theory if quantum corrections to the classical rate expressions are assumed to be temperature independent in the limit when the transition energy is much greater than thermal energy. In this case, the theory indicates that the initial increase in T1 with temperature arises because of a competition between properties of the solvent which are changing rapidly as the temperature is raised above the critical temperature. At sufficiently high temperature, properties of the solvent vary slowly with temperature, and the explicit temperature dependence of the vibrational relaxation dominates, producing a decrease in T1 with increasing temperature. The predictions of the theory are also examined when other postulated forms of the quantum correction factors are used, and the implications of these results for theoretical approaches to vibrational relaxation are discussed. © 1997 American Institute of Physics.
Show PACS
34.50.Ez Rotational and vibrational energy transfer
33.20.Ea Infrared spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants

Femtosecond time-resolved two-photon ionization spectroscopy of K2

H. Schwoerer, R. Pausch, M. Heid, V. Engel, and W. Kiefer

J. Chem. Phys. 107, 9749 (1997); http://dx.doi.org/10.1063/1.475271 (6 pages) | Cited 22 times

Full Text: | Download PDF

Show Abstract
We investigated the coherent motion of vibrational wave packets in the ∣B〉 1Πu state of the potassium dimer applying two color pump/probe spectroscopy with a sub 100 fs time resolution. Special interest was paid to the ionization probe step which was analyzed carefully by varying the probe energy over a wide range. Time-dependent quantum calculations explain the experimental outcomes by introducing a nonconstant transition dipole moment between the ∣B〉 and the ionic state ∣X+〉 and by taking into account the excitation of long lived autoionizing Rydberg states. © 1997 American Institute of Physics.
Show PACS
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Rotational analysis of the math2A′′−math2A′′ origin band of the CH2CFO radical

Scott A. Wright and Paul J. Dagdigian

J. Chem. Phys. 107, 9755 (1997); http://dx.doi.org/10.1063/1.475272 (4 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
The laser fluorescence excitation spectrum of the origin band of an electronic transition in the CH2CFO radical was recorded with partial rotational resolution using a supersonic, rotationally cold beam. The radical was prepared in a pulsed free jet by 193 nm photolysis of acetyl fluoride diluted in helium or argon. The rotational structure of the band is consistent with an in-plane electronic transition of this near oblate rotor. In analogy with the vinoxy radical, this transition is designated as math2A′′−math2A′′. Spectroscopic constants were derived from a fit to the assigned rotational transitions. The lower state rotational constants agree with those calculated from an ab initio CH2CFO equilibrium structure [M. Furubayashi, I. Bridier, S. Inomata, N. Washida, and K. Yamashita, J. Chem. Phys. 106, 6302 (1997)]. The present study thus provides confirmation of the assignment of the molecular carrier as CH2CFO and eliminates the alternative assignment to FCO [B. A. Williams and J. W. Fleming, J. Chem. Phys. 106, 4376 (1997)]. © 1997 American Institute of Physics.
Show PACS
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra
37.20.+j Atomic and molecular beam sources and techniques

A structural model for associated liquid ethanol developed from transient spectroscopy

R. Laenen and C. Rauscher

J. Chem. Phys. 107, 9759 (1997); http://dx.doi.org/10.1063/1.475273 (5 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
We propose a detailed structural model for ethanol oligomers assuming it to form open chains. An inhomogeneous broadening with a width of about 100 cm−1 of the OH-stretching mode of the hydrogen-bonded species is considered, a parabolic increase of the absorption strength and a cubic dependency of the frequency of this vibration with position within the associate. With these asumptions we are able to account for the measured conventional IR absorption spectra of ethanol at different dilutions in CCl4 with the most probable length of the associates ranging between 2 and 13 molecules, respectively. Application of our model to time-resolved spectroscopy on a 0.17 M sample with excitation performed at 3340 cm−1 yields a length of the excited oligomers of 4 to 5 and of broken species of 2 to 3, respectively. © 1997 American Institute of Physics.
Show PACS
82.30.Nr Association, addition, insertion, cluster formation
33.70.Jg Line and band widths, shapes, and shifts
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.70.Dk Environmental and solvent effects
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Raman spectroscopy of the N–C–O symmetric (ν3) and antisymmetric (ν2) stretch fundamentals in HNCO

Steven S. Brown, H. Laine Berghout, and F. Fleming Crim

J. Chem. Phys. 107, 9764 (1997); http://dx.doi.org/10.1063/1.475274 (8 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
We report the first gas-phase Raman spectra of the N–C–O stretching fundamentals in isocyanic acid. Using stimulated Raman excitation to prepare vibrationally excited molecules, we record spectra via two different techniques, photoacoustic Raman spectroscopy and action spectroscopy. The former detects the sound wave generated as the Stokes laser tunes through resonances and deposits heat in the gas sample. The latter detects transitions by photodissociating the vibrationally excited states prepared in the vibrational excitation step and detecting the photofragments by laser induced fluorescence. In analogy with the stretching modes in CO2, the N–C–O symmetric stretch (ν3) Raman fundamental in HNCO is strong while the antisymmetric stretch (ν2) is weak, although neither is symmetry forbidden. Both vibrational states are strongly perturbed. The symmetric stretch interacts with combination states that contain two quanta of bending excitation, and the antisymmetric stretch interacts with several different combination states. Both Raman spectra have strong QQ branch rotational structure in which the band origins for different K sublevels in this near-prolate symmetric top follow no simple pattern. Photodissociation of the vibrationally excited states demonstrates the influence of the initial state preparation on the rotational resonances, photofragment appearance thresholds, and Franck–Condon factors in the transition to a dissociative excited electronic state. © 1997 American Institute of Physics.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra
33.80.Gj Diffuse spectra; predissociation, photodissociation

Optical spectroscopy of jet-cooled FeC between 12 000 and 18 100 cm−1

Dale J. Brugh and Michael D. Morse

J. Chem. Phys. 107, 9772 (1997); http://dx.doi.org/10.1063/1.475275 (11 pages) | Cited 42 times

Full Text: | Download PDF

Show Abstract
Iron monocarbide has been investigated between 12 000 and 18 100 cm−1 in a supersonic expansion by resonant two-photon ionization spectroscopy. Six new electronic states have been identified for which origins relative to the ground state have been determined. Three of these possess Ω′ = 3, one possesses Ω′ = 4, and two possess Ω′ = 2. The Ω′ = 3 state with an origin near 13 168 cm−1 is likely a 3Δ3 state and has been assigned as the analog of the [14.0]2Σ+←X2Σ+ charge transfer transition in CoC. The Ω′ = 4 state is most likely a 3Φ4 state. Additionally, seven bands with Ω′ = 2 have been observed that have proven impossible to systematically group by electronic state. Because every transition rotationally resolved in this study possesses a lower state with Ω = 3, the ground state has been confirmed as arising from an Ω = 3 state that is most likely the Ω = 3 spin orbit component of a 3Δi term derived from a 1δ39σ1 configuration. The ionization energy (IE) of FeC has been determined as 7.74±0.09 eV by varying the wavelength of the ionization photon. When combined with the known IE of Fe and the bond energy of FeC+, the bond energy of FeC is calculated to be 3.9±0.3 eV. Presentation of the results is accompanied by an analysis of the bonding in FeC from a molecular orbital standpoint. © 1997 American Institute of Physics.
Show PACS
33.20.Kf Visible spectra

Role of guest-host intermolecular forces in photoinduced reorientation of dyed liquid crystals

L. Marrucci, D. Paparo, P. Maddalena, E. Massera, E. Prudnikova, and E. Santamato

J. Chem. Phys. 107, 9783 (1997); http://dx.doi.org/10.1063/1.475276 (11 pages) | Cited 40 times

Full Text: | Download PDF

Show Abstract
An experimental study of the photoinduced molecular reorientation of dyed liquid crystals for a set of guest-host combinations is reported. We find large variations in the magnitude of the effect for different dyes but also for different hosts, with polar hosts resulting often significantly more effective than nonpolar ones. The data are interpreted in terms of a kinetic mean-field model for the dye molecule rotational dynamics and interaction with the liquid crystal host. The results point to a significant variation of guest-host intermolecular forces upon photoinduced electronic excitation of dye molecules. This force variation is reflected in a variation of dye molecule physical parameters such as the rotational friction coefficient and the orientational mean-field energy. © 1997 American Institute of Physics.
Show PACS
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
34.20.Gj Intermolecular and atom-molecule potentials and forces

Electronically excited states in size selected solvated alkali metal atoms. II. Isotope effects in the spectroscopy of sodium water and sodium ammonia complexes

Claus Peter Schulz and Claudia Nitsch

J. Chem. Phys. 107, 9794 (1997); http://dx.doi.org/10.1063/1.475277 (7 pages) | Cited 28 times

Full Text: | Download PDF

Show Abstract
The change of spectroscopic properties of sodium-water and sodium-ammonia complexes upon deuteration is investigated. The ionization potential of NaD2O is shifted by 70 cm−1 towards lower energies compared to NaH2O. A shift of 81 cm−1 between NaND3 and NaNH3 is observed again towards lower energies. From these shift the vibrational frequencies for the ground state of the neutral and ionic complex have been estimated. The first electronically excited state (2E) of NaND3 has been investigated by resonant two color two photon ionization. The comparison with the formerly observed NaNH3 spectrum enables us to do an unequivocal assignment of the vibrational structure. © 1997 American Institute of Physics.
Show PACS
31.50.Df Potential energy surfaces for excited electronic states
31.30.Gs Hyperfine interactions and isotope effects
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

Influence of exciton–exciton interaction on one-to-two exciton transitions in molecular aggregates with linear and circular geometries

Gediminas Juzeliūnas and Peter Reineker

J. Chem. Phys. 107, 9801 (1997); http://dx.doi.org/10.1063/1.475278 (6 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
One- to two-exciton transitions have been examined in molecular aggregates with linear and circular geometries at various strengths of the exciton–exciton interaction. For the interaction parameter a sufficiently different from its critical value acrit = 1, the exciton–exciton interaction has been shown to have little influence on the transition dipole moments, as well as on the corresponding transition energies between the one-exciton states and the dissociated two-exciton states. The interaction between the excitons then may be represented in an effective manner by the replacement of the actual number N of molecules per aggregate by a nearby effective number Neff, the latter being a-dependent. Hence, inclusion of the exciton–exciton coupling does not affect substantially the previous analysis of one- to two-exciton transitions based on the model of noninteracting one-dimensional excitons. That is, effects such as the blue shift of the excited-state absorption and the enhancement of nonlinear susceptibilities are not sensitive to the exciton–exciton interaction. These findings are relevant, inter alia, to J-aggregates in which there is no evidence for the coupling parameter a to be in the critical region or beyond. On the other hand, for the critical value of the exciton–exciton interaction (a = acrit), the blue shift is either totally absent in the excited-state absorption, or extremely small compared with the ordinary case. The above is in full agreement with earlier calculation of the pump–probe spectrum showing a weak dependence on the exciton–exciton interaction for a<1, as well as a strong bleaching of the exciton band in the critical region. © 1997 American Institute of Physics.
Show PACS
36.40.Cg Electronic and magnetic properties of clusters
33.70.Jg Line and band widths, shapes, and shifts
71.35.-y Excitons and related phenomena
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

The picosecond timescale relaxation of photoexcited quaterphenyl in solution

P. Matousek, A. W. Parker, M. Towrie, and W. T. Toner

J. Chem. Phys. 107, 9807 (1997); http://dx.doi.org/10.1063/1.475279 (11 pages) | Cited 8 times

Full Text: | Download PDF

Show Abstract
Time-resolved resonance Raman and transient absorption spectra of photoexcited S1 quaterphenyl in solution have been measured in a single series of experiments over a range of probe wavelengths at various time delays and solvent temperatures. Increases of 0.4% in the energy of the 0–0 electronic resonance transition to the higher (Sn) state and 0.1% in some vibrational frequencies are observed to take place on a 17 picosecond timescale following photoexcitation, and electronic and vibrational bandwidths both reduce by a few percent. Comparisons of measured Raman excitation profiles with profiles calculated from the transient absorbance spectra are used to interpret the time dependence of Stokes resonance Raman band intensities. The electronic resonance shift and width change and relaxation of Franck–Condon displacements all contribute. All parameters vary with bath temperature, but bandshifts are small on cooling and the 0–0 resonance shifts to the red. The change in S0–Sn resonance frequency is taken to imply a change in S0–S1 potential and to be a solvation effect which is also responsible for the displacement and Raman frequency shifts. The anti-Stokes Raman band at 766 cm−1 shows additional intensity changes due to population relaxation on two distinct timescales: <1 ps and ∼ 17 ps. The fast component is attributed to intramolecular redistribution of v>1 excitation energy and the slow component to the decay of a hot v = 1 population with an average excess energy of ∼ 60 cm−1 per molecule. This is much smaller than the initial excess photoexcitation energy of ∼ 5000 cm−1 but corresponds to a temperature much greater than indicated by the bandwidth changes, implying a non-equilibrium distribution of vibrational energy whose decay is not limited by thermal diffusion. The slow component of the population relaxation matches approximately with the change in potential in both energy and timescale but no causal connection is identified. This experiment links the dynamics of Raman frequency shifts observed in an excited state molecule directly to a change in electronic potential. It is suggested a similar mechanism may operate in other systems, such as stilbene. © 1997 American Institute of Physics.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
78.30.C- Liquids
78.47.-p Spectroscopy of solid state dynamics
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Highly excited vibrational states of HCP and their analysis in terms of periodic orbits: The genesis of saddle-node states and their spectroscopic signature

Christian Beck, Hans-Martin Keller, S. Yu. Grebenshchikov, Reinhard Schinke, Stavros C. Farantos, Koichi Yamashita, and Keiji Morokuma

J. Chem. Phys. 107, 9818 (1997); http://dx.doi.org/10.1063/1.474226 (17 pages) | Cited 28 times

Full Text: | Download PDF

Show Abstract
We present quantum mechanical bound-state calculations for HCP(math) using an ab initio potential energy surface. The wave functions of the first 700 states, corresponding to energies roughly 23 000 cm−1 above the ground vibrational state, are visually inspected and it is found that the majority can be uniquely assigned by three quantum numbers. The energy spectrum is governed, from the lowest excited states up to very high states, by a pronounced Fermi resonance between the CP stretching and the HCP bending mode leading to a clear polyad structure. At an energy of about 15 000 cm−1 above the origin, the states at the lower end of the polyads rather suddenly change their bending character. While all states below this critical energy avoid the isomerization pathway, the states with the new behaviour develop nodes along the minimum energy path and show large-amplitude motion with H swinging from the C- to the P-end of the diatomic entity. How this structural change can be understood in terms of periodic classical orbits and saddle-node bifurcations and how this transition evolves with increasing energy is the focal point of this article. The two different types of bending motion are clearly reflected by the rotational constants. The relationship of our results with recent spectroscopic experiments is discussed. © 1997 American Institute of Physics.
Show PACS
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
31.50.Df Potential energy surfaces for excited electronic states
31.15.A- Ab initio calculations
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)

Investigation of the pure rotational spectrum of magnesium monobromide by Fourier transform microwave spectroscopy

Kaley A. Walker and Michael C. L. Gerry

J. Chem. Phys. 107, 9835 (1997); http://dx.doi.org/10.1063/1.475280 (7 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The pure rotational spectrum of the free radical MgBr has been measured in its 2Σ+ ground electronic state by Fourier transform microwave spectroscopy. Transitions have been observed for both 24Mg79Br and 24Mg81Br in the v = 0 and v = 1 vibrational states. Rotational and centrifugal distortion constants have been determined for each isotopomer in each vibrational state. Equilibrium rotational constants have been calculated and an accurate equilibrium bond length has been determined. Spin-rotation constants, for both the unpaired electron and the bromine nuclei, have been calculated along with magnetic and nuclear quadrupole hyperfine constants for the bromine nuclei. From these constants, the electronic structure of MgBr has been investigated and comparisons have been made to similar compounds. The unpaired electron spin density on the bromine nucleus has been found to be very small, suggesting that this is a very ionic compound. However, the Mg–Br bond has been found to have more covalent character than the bond in other alkaline earth monobromides. © 1997 American Institute of Physics.
Show PACS
33.20.Sn Rotational analysis
33.20.Bx Radio-frequency and microwave spectra
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.15.Dj Interatomic distances and angles
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.30.Gs Hyperfine interactions and isotope effects
33.15.Pw Fine and hyperfine structure
33.25.+k Nuclear resonance and relaxation
31.50.Df Potential energy surfaces for excited electronic states
33.70.Jg Line and band widths, shapes, and shifts

Photodissociation of C2H at 193 nm: Branching ratios for the formation of C2 in the X 1Σg+, A 1Πu, and B′ 1Σg+ states

Osman Sorkhabi, Victor M. Blunt, Hua Lin, Dadong Xu, Jacek Wrobel, Roosevelt Price, and William M. Jackson

J. Chem. Phys. 107, 9842 (1997); http://dx.doi.org/10.1063/1.475281 (10 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
The ratio of the nascent population of C2 (X 1Σg+) to C2 (A 1Πu) to C2 (B′ 1Σg+) produced from the photodissociation of C2H at 193 nm has been measured using laser induced fluorescence. This technique is typically used to measure rotational and vibrational distributions in a given electronic state. Here, we have extended the technique to measure the relative electronic distributions in the C2 photofragment. From the simultaneous measurement of the Mulliken (X 1Σg+–D 1Σu+) and Freymark (A 1Πu–E 1Σg+) systems, the nascent population ratio of C2 (A 1Πu) to C2 (X 1Σg+) molecules was determined. Similarly, from the measurement of the Deslandres–D’Azumbuja (A 1Πu–C 1Πg) and the LeBlanc (B′ 1Σg+–D 1Σu+) systems, the nascent population ratio of C2 (A 1Πu) to C2 (B′ 1Σg+) was determined. The overall ratio for the production of C2 in the X:A:B′ electronic states was found to be 1:19:1.4. These results along with the results of high quality ab initio calculations of Cui and Morokuma (unpublished) are used to discuss the photodissociation dynamics of C2H at 193 nm. Furthermore, these results should aid in the analysis and modeling of cometary spectra of C2 . © 1997 American Institute of Physics.
Show PACS
33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
82.20.Hf Product distribution
33.50.Dq Fluorescence and phosphorescence spectra

Evidence of rotational autoionization in the threshold region of the photoionization spectrum of CH3

Maritoni Litorja and Branko Ruscic

J. Chem. Phys. 107, 9852 (1997); http://dx.doi.org/10.1063/1.475282 (5 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
The photoionization spectrum of the threshold region of CH3 equilibrated at room temperature has been recorded and compared to the zero electron kinetic energy (ZEKE) spectrum of Blush et al. [J. Chem. Phys. 98, 3557 (1993)]. The ionization onset region is at ∼ 70 cm−1 higher energy than previous high-temperature photoionization work [Chupka and Lifshitz, J. Chem. Phys. 48, 1109 (1967)], but still ∼ 34 cm−1 lower than that implied by invoking only direct ionization. The residual discrepancy can be accounted for by including fully allowed quadrupole-induced and partially allowed dipole-induced rotational autoionization, thus making the observed onset completely congruous with the ZEKE ionization potential. In addition, the fragment appearance potential of CH3+ from CH4 was redetermined by accurate fitting as AP0(CH3+/CH4)=14.322±0.003 eV. With the very precise ZEKE ionization potential, this yields the best current value for the bond dissociation energy in methane, D0(H–CH3)=4.484±0.003 eV = 103.40±0.07 kcal/mol (104.96±0.07 kcal/mol at 298 K). © 1997 American Institute of Physics.
Show PACS
33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Mt Rotation, vibration, and vibration-rotation constants

Influence of chaos on the ionization induced fragmentation dynamics of van der Waals clusters

M. E. Garcia, D. Reichardt, and K. H. Bennemann

J. Chem. Phys. 107, 9857 (1997); http://dx.doi.org/10.1063/1.475283 (7 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
Molecular dynamics simulations based on a self-consistent electronic model are performed to investigate the effect of ionization on the atomic motion of small van der Waals clusters. We find unimolecular dissociation (fragmentation) with time scales in the picosecond range. The dynamics during the relaxation process after ionization turns out to be extremely nonlinear, with fragmentation times which depend strongly on initial conditions. Our calculations show that the largest Liapunov exponent λ+ after ionization is much larger than λ0, the corresponding exponent before ionization. This indicates that the ionization process enhances the nonlinear character of the motion of small clusters. We also determined the distribution of fragmentation times as a function of the vibrational temperature of the clusters before ionization. Since the ionization process creates a state far away from thermodynamical equilibrium, a time-dependent fragmentation probability W(t) is obtained. Furthermore, W(t) reflects the ionization induced chaotic dynamics. © 1997 American Institute of Physics.
Show PACS
36.40.Qv Stability and fragmentation of clusters
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Effects of a quantum-mechanically driven two-state gating mode on the diffusion-influenced bimolecular reactions

Younjoon Jung, Changbong Hyeon, Seokmin Shin, and Sangyoub Lee

J. Chem. Phys. 107, 9864 (1997); http://dx.doi.org/10.1063/1.475284 (14 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The reduced distribution function formalism of diffusion-influenced bimolecular reactions is generalized to incorporate a quantum-mechanical gating mode in the description. An analytical expression for the reaction rate coefficient is obtained in the Laplace transform domain for a general initial condition. For a simple reaction model, the time-dependent reaction rate coefficient and the product yield are calculated numerically for two representative initial conditions. Dependence of the rate coefficient and the product branching ratio on various reaction parameters is discussed. © 1997 American Institute of Physics.
Show PACS
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
02.30.Uu Integral transforms
02.30.Vv Operational calculus
82.20.Pm Rate constants, reaction cross sections, and activation energies

Controlling nonpolar solvation time scales: An instantaneous normal mode viewpoint

T. S. Kalbfleisch and L. D. Ziegler

J. Chem. Phys. 107, 9878 (1997); http://dx.doi.org/10.1063/1.475285 (12 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
The effects of temperature, solvent mass, ground-state solute–solvent interaction potential, and difference potential on the time scale for the decay of an electronic transition energy gap correlation function (ECF) are investigated within the context of a linear instantaneous normal mode (INM) model of fluid dynamics. This correlation function is also known as the solvation autocorrelation. The system described here is the B-state transition of methyl iodide in the nonpolar solvents argon and methane. The required ground- and excited state interaction potentials have been determined in previous experimental spectroscopic studies. The solvation time scale is of the order of 100–200 fs for solvent densities ranging from ρ∗ = 0.08 to ρ∗ = 0.8. The molecular properties responsible for determining the solvation time scale of this nonpolar system are delineated here. Via this INM approach, the nonpolar solvation time scale can be approximated by the ratio of a characteristic solute–solvent separation distance scaled by the shape of the difference potential and the inertial velocity of the solvent particles. The time scale of solvation is found to be independent of the magnitude of the difference potential (solute–solvent coupling strength). Thus by changing the coupling strength and leaving the shape of the difference potential constant, the corresponding electronic absorption spectrum passes from the inhomogeneous to the motional narrowing limit. This is due to the change in the decay time of the static dipole correlation function and not to any change in system dynamics. Only very modest changes in this decay time are found for realistic temperature increases and mass changes of the solvent. Similarly, changes in the ground-state solute–solvent potential are found to have only a minimal effect on the ECF decay time. Finally, if the shape of the difference potential is similar for two different observables in a given solvent, the use of the spectral density of one for the description of the (ultrafast) solvent response of the other observable is rationalized. © 1997 American Institute of Physics.
Show PACS
82.20.Kh Potential energy surfaces for chemical reactions

Long-time tail effect of the velocity correlation on diffusion-controlled reactions

W. Dong

J. Chem. Phys. 107, 9890 (1997); http://dx.doi.org/10.1063/1.475286 (4 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The existence of the long-time tail in the velocity correlation function of a Brownian particle is first discovered from molecular-dynamics simulations and is now well established theoretically and experimentally. In this work, we ask the following question: does this long-time tail have any effect on the kinetics of diffusion-controlled reactions, and if there is any, how the reaction rate is affected, especially in the asymptotic region, t→∞? We will show that this long-time tail can be taken into account by the theory developed recently by Dong and André. The exact asymptotic solutions to the order of t−1/2 are found analytically with Smoluchowski and Collins–Kimball boundary conditions. This allows us to reveal that the long-time tail of the velocity correlation function contributes to the reaction rate an additional term of O(t−1/2) to the long-time limit of the classic Smoluchowski and Collins–Kimball theories. © 1997 American Institute of Physics.
Show PACS
82.20.Db Transition state theory and statistical theories of rate constants

Theoretical study of the Coulombic explosion in doubly charged Xe clusters

Demosthenes C. Athanasopoulos and Kevin E. Schmidt

J. Chem. Phys. 107, 9894 (1997); http://dx.doi.org/10.1063/1.475287 (5 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
In this work we introduce a theoretical model for the description of doubly charged xenon clusters. It is based on the assumption that the charges migrate inside the cluster by isotropic hopping through a Hubbard Hamiltonian. The Xe atoms are considered classical polarizable particles. For their interaction we use a 2-body potential to which we add charge–charge, charge–dipole, and dipole–dipole interactions. The calculations are carried out within the ground state approximation. We perform molecular-dynamics calculations on doubly charged clusters of up to 55 atoms. We investigate the role that the quantum degree of freedom plays on the critical size for the appearance of the doubly charged clusters. The incorporation of the quantum hopping results in a fragmentation energy barrier for clusters larger than the experimentally observed critical size, so that the calculated critical appearance size is in agreement with experiment. © 1997 American Institute of Physics.
Show PACS
36.40.Qv Stability and fragmentation of clusters
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
31.15.xv Molecular dynamics and other numerical methods

Rotational energy analysis for rotating–vibrating linear molecules in classical trajectory simulation

Sang Tae Park, Jeong Hee Moon, and Myung Soo Kim

J. Chem. Phys. 107, 9899 (1997); http://dx.doi.org/10.1063/1.475288 (8 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
A method has been developed to evaluate the rotational energy of a rotating–vibrating linear molecule in classical trajectory simulation. The method is based on our finding that the component of the angular momentum perpendicular to the figure axis which closely approximates the pure rotational angular momentum is a fairly good constant of motion. Classical kinetic energy of the system has been reorganized to separate the rotational and vibrational parts according to the above concept. Time evolution of the rotational energy thus evaluated shows much less irregular behavior than the ones evaluated with the previous methods over a wide range of rotational and vibrational energies. Combined with the method for mode-specific vibrational energy analysis reported previously, the present method allows a reliable separation of the total energy into each degree of freedom. In particular, the accuracy of the present method seems to be good enough for the rotational energy determination at an instantaneous configuration point along a trajectory, enabling the classical study of real time dynamics. © 1997 American Institute of Physics.
Show PACS
82.20.Rp State to state energy transfer
82.20.Fd Collision theories; trajectory models
33.20.Vq Vibration-rotation analysis
33.20.Sn Rotational analysis

Diffusion-controlled reactions in an electric field: Effects of an external boundary and competition between sinks

S. D. Traytak and M. Tachiya

J. Chem. Phys. 107, 9907 (1997); http://dx.doi.org/10.1063/1.475289 (14 pages) | Cited 5 times

Full Text: | Download PDF

Show Abstract
The effect of an external boundary and diffusive interaction between reactants on the rate constant for diffusion-controlled bulk reactions in an external electric field is considered. Appropriate boundary-value problems for “wall–sink” and “sink–sink” systems in an electric field are solved approximately by the method of reflections. Mainly we are interested in calculation of the deviation of the reaction rate constant from the value calculated by Smoluchowski approach. A thorough analysis is made of the time-dependent case of “wall–sink” system in absence of an electric field. It has been shown that the wall effect leads to a nonexponential long time tail for the bulk concentration of diffusing particles. Special attention is given also to the investigation of competitive effect between two sinks which is found to be of interest for many applications. The rigorous theoretical study of this problem provides a way of quantitative estimation of the shadow effect. Drift of diffusing particles in some arrays of ideal sinks is treated as well. © 1997 American Institute of Physics.
Show PACS
82.30.-b Specific chemical reactions; reaction mechanisms
82.40.-g Chemical kinetics and reactions: special regimes and techniques
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.45.-h Electrochemistry and electrophoresis

A new He–CO interaction energy surface with vibrational coordinate dependence. I. Ab initio potential and infrared spectrum

Tino G. A. Heijmen, Robert Moszynski, Paul E. S. Wormer, and Ad van der Avoird

J. Chem. Phys. 107, 9921 (1997); http://dx.doi.org/10.1063/1.475290 (8 pages) | Cited 66 times

Full Text: | Download PDF

Show Abstract
The intermolecular potential energy surface of the He–CO complex including the CO bond length dependence has been calculated using symmetry-adapted perturbation theory (SAPT). The potential has a minimum of ϵm = −23.734 cm−1 with Rm = 6.53 bohr at a skew geometry (ϑm = 48.4°) if the molecular bond length is fixed at the equilibrium value of 2.132 bohr. We have applied the potential in the calculation of bound state levels and the infrared spectrum for the 3He–CO and 4He–CO complexes. The computed ab initio transition frequencies are found to agree within 0.1 cm−1 with experiment. In paper II [J. P. Reid, H. M. Quiney, and C. J. S. M. Simpson, J. Chem. Phys. 107, 9929 (1997)], the potential surface is used to calculate vibrational relaxation cross sections and rate constants. © 1997 American Institute of Physics.
Show PACS
34.20.Gj Intermolecular and atom-molecule potentials and forces
33.20.Tp Vibrational analysis
31.15.A- Ab initio calculations
33.20.Ea Infrared spectra
33.15.Dj Interatomic distances and angles
34.50.Ez Rotational and vibrational energy transfer

A new He–CO interaction energy surface with vibrational coordinate dependence. II. The vibrational deactivation of CO(v = 1) by inelastic collisions with 3He and 4He

J. P. Reid, C. J. S. M. Simpson, and H. M. Quiney

J. Chem. Phys. 107, 9929 (1997); http://dx.doi.org/10.1063/1.475295 (6 pages) | Cited 30 times

Full Text: | Download PDF

Show Abstract
Vibrational relaxation cross-sections and rate constants have been calculated for the deactivation of CO(v = 1) by 3He and 4He on a new intermolecular potential with vibrational coordinate dependence [T. G. A. Heijmen, R. Moszynski, P. E. S. Wormer and Ad van der Avoird, J. Chem. Phys. 107, 9921 (1997)]. The new surface is found to resolve the qualitative discrepancy between theory and experiment which existed in earlier theoretical calculations. The low impact energy regime has also been investigated focussing in particular on impact energies of less than 15 cm−1 above the vibrational (v = 1) threshold. Resonance structure has been found to occur and a comparison is made with an earlier investigation of the low temperature region. © 1997 American Institute of Physics.
Show PACS
34.50.Ez Rotational and vibrational energy transfer
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions
34.20.Gj Intermolecular and atom-molecule potentials and forces
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Describing van der Waals Interaction in diatomic molecules with generalized gradient approximations: The role of the exchange functional
  2. Rotational–translational electrolyte friction on nonspherical particles
  3. O2 transient trapping-desorption at the Ag(111) surface
  4. Order fluctuations in the mesophase of polydiethylsiloxane as studied by the dipolar‐correlation effect on the stimulated echo
  5. The shape, size, aggregation, hydration, correlation times, and thermodynamic studies on macromonomer micelles
Go to AIP Home
Copyright © American Institute of Physics
close